The present invention relates to fiber optic networks and particularly to WDM optical networks which require continued usage of the main fiber path while the wavelength plan is changed.
The public""s increasing demand for bandwidth has contributed to an acceleration in the development of wavelength division multiplexing (WDM) technology. Using WDM, data can be transmitted at a high rate on each of several wavelengths of light sharing an optical fiber. Currently, systems exist in which a single fiber carries over 100 Gb/s of data using 40 or more wavelengths.
Because of the large number of wavelengths and the high data rates involved, it becomes increasingly necessary to find a more flexible way of accessing individual wavelengths of light (optical channels) for purposes of reception at, or transmission from, a given node of a WDM network. Conventionally, individual optical channels may be xe2x80x9cdroppedxe2x80x9d by inserting a filter in the main fiber path which reflects the desired wavelength towards equipment connected to the node where opto-electronic conversion and other processing may take place. Similarly, the addition of an optical channel is typically achieved by the insertion of a filter in the main fiber path, which filter transfers light arriving at the node at a desired wavelength back into the main optical path. When multiple wavelengths are to be dropped or added, multiple optical filters must be inserted in the main optical path at the location of the node.
Since the optical add and drop filters are tuned to specific wavelengths and intercept the optical flow along the main fiber path, it is crucial to provision a conventional WDM network with the correct number, location and operational wavelength of filters upon initial installation. Conventional WDM network architectures are therefore subject to eventual fiber interruptions and to the eventual addition or replacement of equipment in order to keep pace with the evolution of the network and that of the WDM technology used to transmit data through the network.
Given the high data rates involved, any disruption of the main fiber path leads to severe inconveniences for the operator and users of the network, while the operator is further burdened with the cost of adding or replacing equipment. Clearly, what is needed is a network architecture which satisfies current operational requirements while being sufficiently flexible to accommodate evolutionary changes in the network and in the wavelength plan.
According to a first broad aspect, the invention may be summarized as an optical communications node, including an optical coupling device having a first input port and a plurality of output ports and a drop circuit connected to at least one of the output ports. Each drop circuit is arranged to isolate a portion of the optical frequency spectrum of the optical signal present at the output port to which that drop circuit is connected.
The invention may be summarized according to a second broad aspect as a node for use in an optical communications network, including an optical coupling device having a plurality of input ports and an output port and an add circuit connected to at least one of the input ports, for admitting a signal occupying a selected portion of the optical frequency spectrum.
According to a third broad aspect, the invention may be summarized as a bidirectional node for use in an optical communications network, including an optical coupling device having a plurality of bidirectional first ports and a plurality of bidirectional second ports and a bidirectional optical filtering circuit connected to at least one of the first ports. At least another one of the first ports and at least one of the second ports are connectable to a main optical path, while the wavelengths of optical signals coupled to the main optical path by the filtering circuit and the optical coupling device are selected to be substantially non-interfering with respect to wavelengths occupied by optical signals arriving at the node along the main optical path.
The invention may also be summarized broadly as a node for use in a fiber optic network, including a broadband optical coupler having at least one input port and a plurality of output ports, the coupler being characterized by a through loss LTHROUGH. The node also has a unit for measuring the optical power PINxe2x80x94CURRENT of a multi-channel optical signal present at said input port of said coupler, an amplification unit for amplifying said multi-channel optical signal in accordance with a gain and a processing unit connected to the amplification unit. The processing unit is operable to receive control information comprising at least the output power level POUTxe2x80x94PREV of a previous node in the network and to set said gain equal to a function of POUTxe2x80x94PREV, PINxe2x80x94CURRENT, LTHROUGH and a local target power level TLOCAL.
According to yet another broad aspect, the invention may be summarized as a node for connection between first and second adjacent nodes in a main optical traffic-carrying path. The node includes a plurality of first ports and a plurality of second ports, at least one of the first ports being connectable to the first adjacent node and at least one of the second ports being connectable to the second adjacent node. The node also includes an optical coupling device arranged such that light entering any of the first ports is coupled to each of the second ports and light entering any of the second ports is coupled to each of the first ports, as well as removable filtering circuits connected to at least one of the first ports not connected to the first adjacent node and at least one of the second ports not connected to the second adjacent node. The filtering circuits are adapted to add or drop specified wavelength channels to or from the main optical path.
Due of the use of broadband couplers in the various nodes, this method advantageously allows accurate control of the loss around the ring, as the through loss of the couplers is generally known at each node.
The invention also extends to nodes equipped with power measurement devices and processors operable to execute the above described method.